feat: reimplement clone for find and aggregate cursors

NODE-2811

Author: mbroadst

src/cursor/aggregation_cursor.ts

@@ -48,6 +48,16 @@ export class AggregationCursor extends AbstractCursor {
     return this[kPipeline];
   }
 
+  /**
+   * Returns a new unitialized copy of this cursor, with options matching those that have been set on the current instance
+   */
+  clone(): AggregationCursor {
+    return new AggregationCursor(this[kParent], this.topology, this.namespace, this[kPipeline], {
+      ...this[kOptions],
+      ...this.cursorOptions
+    });
+  }
+
   /** @internal */
   _initialize(session: ClientSession | undefined, callback: Callback<ExecutionResult>): void {
     const aggregateOperation = new AggregateOperation(this[kParent], this[kPipeline], {

src/cursor/find_cursor.ts

@@ -49,6 +49,16 @@ export class FindCursor extends AbstractCursor {
     }
   }
 
+  /**
+   * Returns a new unitialized copy of this cursor, with options matching those that have been set on the current instance
+   */
+  clone(): FindCursor {
+    return new FindCursor(this.topology, this.namespace, this[kFilter], {
+      ...this[kBuiltOptions],
+      ...this.cursorOptions
+    });
+  }
+
   /** @internal */
   _initialize(session: ClientSession | undefined, callback: Callback<ExecutionResult>): void {
     const findOperation = new FindOperation(undefined, this.namespace, this[kFilter], {

test/functional/abstract_cursor.test.js

@@ -22,7 +22,7 @@ describe('AbstractCursor', function () {
   before(
     withClientV2((client, done) => {
       const docs = [{ a: 1 }, { a: 2 }, { a: 3 }, { a: 4 }, { a: 5 }, { a: 6 }];
-      const coll = client.db().collection('find_cursor');
+      const coll = client.db().collection('abstract_cursor');
       const tryNextColl = client.db().collection('try_next');
       coll.drop(() => tryNextColl.drop(() => coll.insertMany(docs, done)));
     })
@@ -160,34 +160,74 @@ describe('AbstractCursor', function () {
     );
   });
 
-  context('#rewind', function () {
-    beforeEach(
+  context('#clone', function () {
+    it(
+      'should clone a find cursor',
       withClientV2(function (client, done) {
-        const coll = client.db().collection('rewind');
-        coll.drop(() => {
-          coll.insertMany([{}, {}], err => {
+        const coll = client.db().collection('abstract_cursor');
+        const cursor = coll.find({});
+        this.defer(() => cursor.close());
+
+        cursor.toArray((err, docs) => {
+          expect(err).to.not.exist;
+          expect(docs).to.have.length(6);
+          expect(cursor).property('closed').to.be.true;
+
+          const clonedCursor = cursor.clone();
+          this.defer(() => clonedCursor.close());
+
+          clonedCursor.toArray((err, docs) => {
+            expect(err).to.not.exist;
+            expect(docs).to.have.length(6);
+            expect(clonedCursor).property('closed').to.be.true;
+            done();
+          });
+        });
+      })
+    );
+
+    it(
+      'should clone an aggregate cursor',
+      withClientV2(function (client, done) {
+        const coll = client.db().collection('abstract_cursor');
+        const cursor = coll.aggregate([{ $match: {} }]);
+        this.defer(() => cursor.close());
+
+        cursor.toArray((err, docs) => {
+          expect(err).to.not.exist;
+          expect(docs).to.have.length(6);
+          expect(cursor).property('closed').to.be.true;
+
+          const clonedCursor = cursor.clone();
+          this.defer(() => clonedCursor.close());
+
+          clonedCursor.toArray((err, docs) => {
             expect(err).to.not.exist;
+            expect(docs).to.have.length(6);
+            expect(clonedCursor).property('closed').to.be.true;
             done();
           });
         });
       })
     );
+  });
 
+  context('#rewind', function () {
     it(
       'should rewind a cursor',
       withClientV2(function (client, done) {
-        const coll = client.db().collection('rewind');
+        const coll = client.db().collection('abstract_cursor');
         const cursor = coll.find({});
         this.defer(() => cursor.close());
 
         cursor.toArray((err, docs) => {
           expect(err).to.not.exist;
-          expect(docs).to.have.length(2);
+          expect(docs).to.have.length(6);
 
           cursor.rewind();
           cursor.toArray((err, docs) => {
             expect(err).to.not.exist;
-            expect(docs).to.have.length(2);
+            expect(docs).to.have.length(6);
 
             done();
           });
@@ -198,7 +238,7 @@ describe('AbstractCursor', function () {
     it(
       'should end an implicit session on rewind',
       withClientV2(function (client, done) {
-        const coll = client.db().collection('rewind');
+        const coll = client.db().collection('abstract_cursor');
         const cursor = coll.find({}, { batchSize: 1 });
         this.defer(() => cursor.close());
 
@@ -218,7 +258,7 @@ describe('AbstractCursor', function () {
     it(
       'should not end an explicit session on rewind',
       withClientV2(function (client, done) {
-        const coll = client.db().collection('rewind');
+        const coll = client.db().collection('abstract_cursor');
         const session = client.startSession();
 
         const cursor = coll.find({}, { batchSize: 1, session });